Fluorometric determination of cephalexin in urine

A rapid first-derivative spectrophotometric analysis of cephalexin and cephradine in human urine

A rapid, simple, and accurate first-derivative spectrophotometric method has been established for the determination of either cephalexin or cephradine in urine. Quantitative analysis of each antibiotic was achieved by measuring the peak amplitude at 268 nm. The relative and absolute recoveries ranged from 98.90 to 104.00% for cephalexin and from 97.85 to 105.10% for cephradine. The within-day coefficient of variation varied from 3.27 to 6.45%. The applicability of the method for the determination of the cumulative amount of either cephalexin or cephradine excreted unchanged in urine, following an oral dose containing 500 mg of the drug to a human male volunteer, is demonstrated.

High performance liquid chromatographic analysis of cephalexin in serum and urine

A rapid, highly sensitive high performance liquid chromatographic method has been developed for the determination of cephalexin in serum and urine. Serum protein was precipitated with 1% zinc sulphate solution containing cephradine as the internal standard. The drugs were eluted from a 5 micron, C-18 reversed-phase column at ambient temperature with a mobile phase consisting of acetonitrile-methanol-acetate buffer of pH 4.2 (10:10:80%), at a flow rate of 1.4 ml/min with ultraviolet detection at 254 nm. Each analysis lasted 9 min. Quantification was achieved by the measurement of the peak-height ratio and the relative and absolute recoveries varied from 98 to 103%. Detection limits for cephalexin were 1 microgram/ml in serum and 5 micrograms/ml in urine. Within-run coefficient of variation ranged from 0.73 to 5.63% at three different concentrations for the serum and urine assay.

Kinetics and mechanism of in vitro uptake of amino-beta-lactam antibiotics by rat small intestine and relation to the intact-peptide transport system

By utilizing the everted jejunum of rats, the initial uptake rates of several antibiotics were measured over a wide range of concentrations. The uptakes followed mixed-type kinetics involving saturable and non-saturable processes in parallel. The pertinent kinetic parameters for the uptake of each antibiotic were determined. The effect of cephalexin on the uptake of cyclacillin obeyed competitive inhibition kinetics, and the inhibition constant Ki was found to be equal to the Michaelis constant Kt for the uptake of cephalexin itself. In a similar way, the uptake of cephalexin was inhibited by cyclacillin. Uptakes of both cyclacillin and cephalexin were reduced significantly by several metabolic inhibitors. From the effect of temperature on the uptakes of cyclacillin and cephalexin, activation energies of 24.8 and 23.1 kcal/mole were obtained respectively. These results indicate the involvement of an active transport mechanism for cyclacillin and cephalexin. It was found that several dipeptides markedly inhibited the uptakes of cyclacillin and cefadroxil. Furthermore, the uptake of glycylglycine, a typical dipeptide, was inhibited by cyclacillin, cefadroxil, cephalexin, and cephradine. The kinetics of mutual inhibition of the uptakes of cyclacillin and glycylglycine were consistent with competitive-type inhibition. This is the first report which establishes, from a kinetic point of view, the involvement of a common transport system in the in vitro uptakes of the dipeptides and the antibiotics.

High-performance liquid chromatographic method for determination of cefmetazole in human serum

A fast, specific, sensitive high-performance liquid chromatographic method for the determination of cefmetazole in human serum was developed. The serum samples were deproteinized by adding 5% trichloroacetic acid in methanol containing barbital as an internal standard and were injected onto a reverse-phase column (mu-Bondapak C18) with a mobile phase of 10 to 15% acetonitrile in 0.005 M citrate buffer (pH 5.4). Eluted components were detected by UV absorption at 254 nm. Cefmetazole and the internal standard were separated from interfering serum components by this method. The peak height ratio of cefmetazole to the internal standard was proportional to the cefmetazole concentration in the range from 0.4 to 100 micrograms/ml. Serum samples obtained from three patients after a single intravenous injection of cefmetazole were assayed by this method and by a microbiological method. There was a good correlation between two assay methods (correlation, coefficient, 0.98). The stability of cefmetazole in human serum was (correlation coefficient, 0.98). The stability of cefmetazole in human serum was also determined by this method. Cefmetazole was stable in human serum for 2 weeks at 4 degrees C or for at least 8 weeks if it was kept frozen. As the high-performance liquid chromatography method is simple, specific, accurate, and reproducible, it appears to be more suitable for routine assay of cephalosporins than other assay methods.

Isolation and identification of the fluorescent degradation product of some beta-lactam antibiotics

A fluorescent degradation product of cephalexin, recently employed in the determination of this antibiotic in aqueous solution and human plasma, has been isolated and identified as 2-hydroxy-3-phenyl-6-methylpyrazine. Spectroscopically and chromatographically the product is indistinguishable from that obtained by the same method from a series of other cephalosporins and penicillins bearing an alpha-amino group on the side-chain, and from the pyrazine structure produced by synthesis. Two reported methods for the fluorimetric determination of ampicillin have also been found to yield the same degradation product and not the suggested diketopiperazine structure.